A gallium nitride compound semiconductor is frequently used as devices such as light emitting diodes and laser diodes. The production process of a gallium nitride compound semiconductor (the gallium nitride compound semiconductor process) is typically conducted by vapor-growing a gallium nitride compound on a substrate such as a sapphire substrate through the MOCVD process. As source gas used for the gallium nitride compound semiconductor process, trimethylgallium, trimethylindium, and trimethylaluminum that contain a group III element and ammonia that contains a group V element are used.
Generally, commercially available industrial crude ammonia (industrial crude ammonia) contains hydrogen, nitrogen, oxygen, carbon dioxide, water, etc. Moreover, relatively highly pure ammonia is commercially available, which is obtained by further distilling or rectifying the crude ammonia or by diluting the crude ammonia with highly pure inert gas. However, the gallium nitride compound semiconductor process requires ultrapure ammonia as source material obtained by further purifying relatively highly pure ammonia obtained after industrial ammonia is distilled or rectified.
Conventionally, a method of purifying crude ammonia by using a nickel catalyst, etc. has been developed. For example, JP H05-124813 A and JP H06-107412 A disclose a method of continuously purifying crude ammonia, in which the crude ammonia is brought into contact with a catalyst containing nickel as the main component to remove impurities. Moreover, JP 2002-37624 A discloses a method of continuously purifying and supplying industrial crude ammonia to the gallium nitride compound semiconductor process, in which the crude ammonia is brought into contact with a catalyst containing nickel as an active component and then with synthetic zeolite having a pore size equivalent to from 4 to 10 A to remove impurities contained in the crude ammonia.
On the other hand, JP 2008-7378 A discloses a method of recovering ammonia contained in discharge gas discharged from the gallium nitride compound semiconductor process, in which ammonia contained in the discharge gas is dissolved in water, and the aqueous ammonia in which ammonia is dissolved in water is distilled to separate ammonia from water, and the separated ammonia is liquefied. JP 2013-245131 A discloses a method of recovering ammonia, in which the discharge gas is subjected to a pressurizing process and a cooling process with a heat pump to liquefy and separate ammonia from hydrogen and nitrogen to recover ammonia.
Moreover, JP 2014-5181 A discloses a method of purifying ammonia, in which impurities causing an negative effect on the vapor deposition speed, etc. are removed from inexpensive commercially available industrial crude ammonia without distillation or rectification to continuously supply ammonia to the gallium nitride compound semiconductor process, in which the crude ammonia is brought into contact with a filter, with activated carbon to remove oil contained in the crude ammonia, and then with a catalyst containing nickel as an active component and with synthetic zeolite to remove the impurities other than oil.
JP 2014-37333 A also discloses a method of purifying ammonia, in which impurities causing an negative effect on the vapor deposition speed, etc., are removed from the inexpensive commercially available industrial crude ammonia without distillation or rectification to continuously supply ammonia to the gallium nitride compound semiconductor process, including the steps of: bringing the crude ammonia into contact with an oil removing means to remove oil contained in the crude ammonia, measuring the presence or the absence of oil or the concentration of oil in the crude ammonia after the oil removing step and bringing the crude ammonia after the measuring step into contact with a catalyst containing nickel as an active component and with synthetic zeolite to remove the impurities other than oil.
When conventional oil measurement is repeated, the oil sampling pipes have to be replaced at each measurement. This makes the operation complicated. Furthermore, accurate and delicate measurement is difficult due to an influence of impurities such as oil out of the tools when the oil sampling pipes are replaced. Then, JP 2014-62815 A discloses an oil measuring device and an oil measuring method that are capable of easy, accurate, and delicate measurement. The oil measuring device measures the amount of oil contained in ammonia gas, which is provided with an adsorption cylinder filled with an oil adsorbent and an analysis part analyzing oil desorbed from the adsorbent. The oil measuring method of measuring the amount of oil contained in ammonia gas includes the steps of bringing ammonia gas into contact with an adsorbent, adsorbing oil contained in ammonia gas to the adsorbent, desorbing oil adsorbed to the adsorbent, and analyzing the desorbed oil.